On Fri, 28 Mar 2014, Viresh Kumar wrote:
> Hi Thomas,
>
> I couldn't understand one part of hrtimer (obviously there are
> others as well, but here I am sure I couldn't understood it :)).
>
> In switch_hrtimer_base() we are calling hrtimer_check_target()
> which guarantees this:
>
> /*
> * With HIGHRES=y we do not migrate the timer when it is expiring
> * before the next event on the target cpu because we cannot reprogram
> * the target cpu hardware and we would cause it to fire late.
> *
> * Called with cpu_base->lock of target cpu held.
> */
>
> But switch_hrtimer_base() is only called from one place, i.e.
> __hrtimer_start_range_ns() and at the point (where we call
> switch_hrtimer_base()) expiration time is not yet known as
> we call this routine later:
>
> hrtimer_set_expires_range_ns()
>
> So, do we really need to call hrtimer_check_target() at all
> in switch_hrtimer_base()? Or do we need to move
> hrtimer_set_expires_range_ns() before calling
> switch_hrtimer_base() ??
Yes, we should move setting the expiry time before we call
switch_hrtimer_base().
Thanks,
tglx
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